Electrically conductive polypyrroleamine polymer networks

ABSTRACT

Electrically conductive polyaminopyrrole polymer networks are provided comprising conjugated crosslinks between polyaminopyrrole polymer segments of the network. The network can be formed by crosslinking amine functional polyaminopyrrole polymers, such as by crosslinking condensation reaction with conjugated polyketone crosslinkers. The amine functional polyaminopyrrole polymers can be prepared by polymerization, such as by electropolymerization of amine functional pyrrole monomers (the amine functionality generally being protected during polymerization) and, optionally, suitable conjugated copolymerization monomers such as thiophene, pyrrole and/or amine functional thiophene.

INTRODUCTION

The present invention relates to novel polymer networks and, moreparticularly, to polyaminopyrrole polymer networks having electricalconductivity.

BACKGROUND OF THE INVENTION

Electrically conductive polymers are increasingly finding application inelectrical and electronic devices, for example, as organic electrodesand the like. Enhanced conductivity is desirable to lower dissipationand, more generally, to meet the needs of more demanding applications.Electrically conductive polymers are commonly made byelectropolymerization at an electrode. Typically, essentially insolublefilms are produced from suitable unsaturated reactant materials formingconjugated polymer chains. The polymer chains can be made conductive, ormore conductive, by doping with known materials, such as iodine, AsF₆anions, etc. The dopant is thought to facilitate the transfer of charge(electrons or holes) along the conjugated polymer chain or, to a limitedextent, from one polymer chain to another. Conductivity is thought to belimited by such chain-to-chain hopping processes. In principle, higherconductivities would perhaps be achievable by increasing the length ofthe conjugated polymer chains. If conjugated chains suitable forconductive polymers are made by electrode polymerization of reactantmonomers in a good solvent for the short polymer chains, they willdissolve from the surface of the electrode into the solvent resulting indisadvantageously short polymer chains. Typically, electropolymerizationsynthesis procedures result in relatively short conjugation length.

Also, the polymerization process typically generates polymers with acertain level of defects in the conjugation, for example, through theintroduction of sp³ carbons into the backbone of the polymer intended tobe conjugated entirely through unsaturated sp² and/or sp sites. Suchdefects in the polymerization process limit the conductivity of thepolymer material. Conductive polymers may be prepared using conventionalsolution based polymerization processes. These processes are known tosuffer potentially the disadvantage of generating the above mentionedsp³ defects in the polymer backbone, reducing the conductivity of thepolymer.

The use of electropolymerization to produce conducting polypyrrolepolymer films is discussed by Diaz et al in Electrochemistry ofConducting Polypyrrole Films, J. Electroanal. Chem., 129 (1981) 115-132.The Diaz et al article describes the electropolymerization reactionprocess and reports the production of polypyrrole polymer films whichare highly conducting when in the oxidized state. Specifically,polypyrrole polymer films are prepared by electropolymerization ofpyrrole on a platinum electrode surface in an acetonitrile electrolytesolution. In addition, the preparation of poly-N-methylpyrrole andpoly-N-phenylpyrrole films are described.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, electricallyconductive polymer networks are provided, specifically, novelpolyaminopyrrole polymer networks. More specifically, thepolyaminopyrrole polymer networks of the invention, which may compriseconductivity enhancing dopant, have conjugated crosslinking betweenconjugated polyaminopyrrole polymer segments within the network.Transfer of charge carriers in the network functions along theconjugated polymer backbone segments by the same mechanisms foundapplicable to corresponding single chain polymers. While not wishing tobe bound by theory, conductivity in the polymer networks of the presentinvention is presently understood to be enhanced by the conjugatedcrosslinks. The conjugated crosslinks provide, in effect, anuninterrupted conjugated structure with the conjugated polyaminopyrrolepolymer backbone segments, thus bypassing any sp³ defects. Certainembodiments of the invention provide electrically conductive polymernetworks suitable for use in electrical and electronic devices and/orhave properties, such as non-linear optical effects, suitable forapplication in electro-optical switches, modulators or sensors. One suchpreferred application for electrically conductive polymer networks ofthe invention is as gasket material to provide EMF shielding.

According to another aspect of this invention, the polyaminopyrrolepolymer network is formed as the condensation crosslinking reactionproduct of amine functional polyaminopyrrole polymers with a conjugatedcrosslinker as a second reactant.

According to another aspect of the invention, the amine functionalpolyaminopyrrole polymers are the polymerization reaction product ofreactant monomers comprising amine functional pyrrole monomers and,optionally, conjugated copolymerization monomers. Preferably suchpolymerization is carried out by electropolymerization of the reactantmonomers. As discussed further below, the amine functional group may belabile, and should be reversibly protected by a protecting group duringthe polymerization reaction. The free amine functionality is thenregenerated subsequent to polymerization for the crosslinking reaction.Additional aspects and advantages of the invention will be betterunderstood in light of the following discussion wherein certainpreferred embodiments of the invention are described in detail.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

It will be understood from the foregoing summary of the invention andfrom the following description of preferred embodiments, that thepolyaminopyrrole polymer network generally will not have free aminefunctionality. It is generally preferred that all or substantially allfree amine functionality be consumed in condensation crosslinkingreaction to form conjugated crosslinks between the conjugated polymersegments of the network. Thus, the term polyaminopyrrole polymer networkis used to mean the network which can be prepared as the conjugatedcrosslinked reaction product of amine functional polyaminopyrrolepolymers and/or equivalent or analogous chemical entities by whateversynthesis route produced.

The polyaminopyrrole polymer segments of preferred polymer networks ofthe invention are fully conjugated via sp² sites. That is, they provide,ideally, an uninterrupted path of conjugated bonds along substantiallytheir entire length. In accordance with known techniques, themonomer-to-monomer bonds of the polymer segments preferably are locatedin each instance between the carbon atoms adjacent to the nitrogen atomof the pyrrole ring. The polymer networks optionally comprise dopantmaterial to enhance electrical conductivity. Numerous suitable dopantmaterials are well known and will be apparent to those skilled in theart in view of the present disclosure. Exemplary dopant materials foruse in the polymer networks of the present invention include iodine,AsF₆ anions and the like. In that regard, it should be understood thatall references herein to reactant monomers, including both aminefunctional pyrrole and the conjugated copolymerization monomersdiscussed further below, may be substituted in accordance with theteachings of U.S. Pat. No. 4,929,389 to produce self-doped polymers.Certain preferred embodiments of the polyaminopyrrole polymer networksof the present invention are doped to have greater electricalconductivity.

Similarly, it should be understood that the amine functional pyrrolemonomers and/or the conjugated copolymerization monomers may be modifiedto provide enhanced solubility in water in accordance with thetechnology of U.S. Pat. No. 4,929,389, the teaching of which isincorporated herein by reference. Thus, reference below to pyrrolemonomers will be understood to include analogous monomers having, forexample, an alkyl group substituted for a hydrogen atom located in thebeta position of the pyrrole ring and having a surfactant molecule atthe end of the alkyl chain. In addition, in accordance with suchteaching, resultant polymers of this type having 8 or more carbon atomsin the alkyl chain in certain embodiments exhibit liquid crystallinebehavior, resulting in high electrical anisotropy. Of course, suchfunctionality must be selected so as to be compatible with thepolymerization and crosslinking reactions employed to produce thepolyaminopyrrole polymer networks of the invention.

In addition to the fully conjugated polyaminopyrrole polymer segments,it is a highly significant additional feature of the polymer networks ofthe invention that they comprise conjugated crosslinks, meaningcrosslinks forming uninterrupted conjugation between thepolyaminopyrrole polymer segments. The short conjugated crosslinks ofthe invention significantly enhance electrical conductivity in thenetwork. Without wishing to be bound by theory, it is presentlyunderstood that the conjugated crosslinks provide an essentiallyinfinite conjugated structure wherein innumerable parallel andalternative conductivity paths are provided to overcome or minimize theeffect of any conjugation defects (e.g., sp³ link defects) in thepolyaminopyrrole polymer segments, i.e., the backbone segments of thenetwork.

In view of the present disclosure, various suitable synthesis routeswill be apparent to those skilled in the art for preparing thepolyaminopyrrole polymer networks of the invention. In accordance withcertain preferred embodiments of the invention, synthesis of suchpolymer networks is accomplished by the condensation crosslinkingreaction of amine functional polyaminopyrrole polymers. The aminefunctional polyaminopyrrole polymers preferably have an average polymerchain length of 20 to 30 monomer units and are the electropolymerizationreaction product of reactant monomers comprising amine functionalpyrrole monomers and, optionally, conjugated copolymerization monomersin mole ratio of from 1:20 to 20:1. It will be understood by thoseskilled in the art that reference herein to the pyrrole monomers asbeing "amine functional" is intended to include both pyrrole monomershaving free amine functionality and those having amine functionalitywhich has been reversibly protected by reaction with a protecting group.Under some polymerization procedures, including someelectropolymerization procedures, the amine group may be labile. Theamine group preferably is protected as the imine, which may be preparedby reacting the monomer with acetone or similar low molecular weightketone in the presence of pTSA or the like. The free amine can beregenerated after polymerization, generally by acid hydrolysis.

Preferred amine functional pyrrole monomers include unsubstituted2-aminopyrrole, 3-aminopyrrole and mixtures thereof. In view of thepresent disclosure, the suitability of numerous analogues and otherequivalent monomers including, for example, substituted aminopyrrolemonomers such as Cl or other halide substituted aminopyrrole monomers,will be apparent to those skilled in the art. Preferably, the aminefunctional monomers are polymerized together with conjugatedcopolymerization monomers, for example, thiophene, pyrrole, aminefunctional thiophene (the amine functionality generally being protectedduring the polymerization reaction) and any mixture thereof. Othersuitable conjugated copolymerization monomers will be apparent to thoseskilled in the art, who also will recognize that conjugatedcopolymerization monomers need not be employed in the polymerization. Tocontrol the degree of crosslinking, however, it is preferred to employnon-crosslinking functional copolymerization monomers, such as pyrroleand pyrrole, together with the amine functional monomers in a ratio offrom about 1:20 to about 20:1. More preferably, the non-functionalconjugated copolymerization monomers are used with aminopyrrole monomersin a ratio of from about 20:1 to about 1:1.

Suitable electropolymerization reaction procedures for preparing thecrosslinkable amine functional polyaminopyrrole polymers are familiar tothose skilled in the art, and are carried out for polymerization in thepresent invention with well known materials and techniques. Suitablematerials and techniques are disclosed for example, in the Diaz et alarticle identified above, the disclosure of which is incorporated hereinby reference. There are numerous commercially available solventssuitable for such electropolymerization. Exemplary solvents includeDMSO, methyl pyrrolidine, DMF, acetonitrile and other highly polarsolvents. Additional suitable solvents will be readily apparent to thoseskilled in the art in view of the present disclosure. The aminefunctional polyaminopyrrole polymers may also be prepared usingconventional solution-based polymerization processes. Again, suchprocesses are well known to those skilled in the art and will be readilyapplied to this invention in view of the present disclosure. In anelectropolymerization process, the polyaminopyrrole polymer generallywill not form a deposited film on the surface of the electrode. Thiswill depend in part on the solubility of the polymer in the solvent usedin the electropolymerization process. In certain applications, however,it may be desirable to form the electrically conductive polyaminopyrrolenetwork on the surface of a workpiece suitable for use as an electrodein the electropolymerization process. In one such application, apolyaminopyrrole polymer network film is formed as an electricallyconductive film on a glass surface intended for use as an electrochromicpanel. Where the electropolymerization takes place in a solvent which isa good solvent for the resulting amine functional polyaminopyrrolepolymers, the polymerized chains will be dissolved from the surface ofthe electrode at which they are formed during the electropolymerizationprocess. In accordance with certain preferred embodiments of theinvention, the amine functional polyaminopyrrole polymers have anaverage polymer chain length of 20 to 30 monomer units.

Crosslinking of the amine functional polyaminopyrrole polymers can beaccomplished by condensation reaction of the amine functionality. Theterm "conjugated crosslinkers" and all related terms used in thisdiscussion will be understood by those skilled in the art to meancrosslinkers which provide an unbroken path of conjugation from onepolymer segment to another within the polyaminopyrrole polymer network.Preferred crosslinkers generate --C═N-- crosslinks that are inconjugation within the crosslinker as well as with the polymer chainsbeing crosslinked. This provides the uninterrupted network ofconjugation, and the advantages resulting therefrom, discussed above.This feature represents a highly significant advance in the art overcorresponding uncrosslinked polymers, which may have unintendedconjugation defects etc., as discussed above, and even over conjugatedpolymer segments in a network having non-conjugated crosslinks. Inaccordance with certain embodiments of the invention, the crosslinkingreaction mixture, optionally including dopant, after deprotecting thepolymers, can be applied in the unreacted, that is, uncrosslinked,condition to a workpiece intended to receive an electrically conductivepolymer coating, gasket, etc. After application to such workpiecesurface, the crosslinking reaction can proceed, optionally with heating,resulting in a hardened, or at least form-stable, electricallyconductive polymer network layer. Numerous other uses and alternativemodes of application will be apparent to those skilled in the art inview of the present disclosure.

In accordance with certain preferred embodiments of the invention,crosslinking is accomplished by condensation reaction of the aminefunctional group of the polyaminopyrrole polymers with unsaturatedconjugated polycarbonyl functional crosslinker, such as unsaturatedpolyaldehyde functional crosslinker or polyketone, most preferably anunsaturated diketone crosslinker. The crosslinking agent may be addedneat or with solvent. Suitable crosslinking agents are commerciallyavailable and/or readily prepared, and will be apparent to those skilledin the art in view of the present disclosure. Preferred unsaturateddiketones include, for example, benzoquinone, especially1,4-benzoquinone, its CN and Cl derivatives, and like members of thegeneral class of naphthoquinones, anthraquinones, etc. The conjugatedcrosslinker may be a suitably functionalized polymer. That is, thecrosslinking functionality may be provided as free functionality on apolymer chain, for example, as free carbonyl functionality on apolythiophene or polypyrrole polymer. Such polymers can be prepared bypolymerization, for example by electropolymerization, of thiopheneand/or pyrrole monomers carrying a suitable (optionally protected)carbonyl group. Exemplary polymer crosslinkers include the 20-30 monomerunit electropolymerization reaction product of2-thiophenecarboxaldehyde, 3-thiophenecarboxaldehyde,pyrrole-2-carboxaldehyde, pyrrole-3-carboxaldehyde or a mixture of anyof them. The carboxaldehyde should be protected as the acetal duringelectropolymerization (e.g., by prior reaction with ethylene glycol orthe like in the presence of PTSA and then returned to the free carbonylby acid hydrolysis after electropolymerization. Numerous such polymercrosslinkers and their preparation and use will be apparent to thoseskilled in the art in view of the present disclosure, the significantfeature being, as discussed above, creation of an unbroken path ofconjugation within and between the polymer segments of the network.

The crosslinking reaction employing polyketone crosslinker may becarried out using techniques well known to those skilled in the art,preferably in a suitable solvent, for example, benzene or toluene. Suchtechnique is applicable, for example, to crosslinking amine functionalpolyaminopyrrole polymers formed in an electropolymerization process, asdiscussed above, or other conventional polymerization techniques.Preferably heat is added to the crosslinking reaction, both to increasethe rate of reaction and to drive off solvents and by-products, such asH₂ O, produced by the reaction between amine and ketone functionality.Solvents such as benzene, toluene and the like, which form lowtemperature aziotropes with water, are preferred, since they willfacilitate reaction by removal of water.

The foregoing description of the invention has presented certainpreferred embodiments for purposes of illustration. The description ofsuch preferred embodiments is not intended to be exhaustive or to limitthe scope of the invention. Various modifications are possible, many ofwhich will be apparent to those skilled in the art in view of the aboveteaching, without departing from the true scope of the invention whichis intended to be defined by the following claims.

We claim:
 1. An electrically conductive polyaminopyrrole polymer networkcomprising conjugated crosslinking between polyaminopyrrole polymersegments.
 2. The electrically conductive polyaminopyrrole polymernetwork of claim 1 comprising the condensation crosslinking reactionproduct of amine functional polyaminopyrrole polymers with conjugatedpolycarbonyl crosslinker.
 3. The electrically conductivepolyaminopyrrole polymer network of claim 2 wherein the amine functionalpolyaminopyrrole polymers have an average polymer chain length of 20 to30 monomer units and are the electropolymerization reaction product ofreactant monomers comprising amine functional pyrrole monomers andconjugated copolymerization monomers in mole ratio of from 1:20 to 20:1.4. The electrically conductive polyaminopyrrole polymer network of claim3 wherein the amine functional pyrrole monomers are selected from thegroup consisting of 2-aminopyrrole, 3-aminopyrrole and mixtures thereof.5. The electrically conductive polyaminopyrrole polymer network of claim4 wherein the amine functional pyrrole monomers are the protectingreaction product of 2-aminopyrrole, 3-aminopyrrole, and any mixturethereof with acetone.
 6. The electrically conductive polyaminopyrrolepolymer network of claim 3 wherein the conjugated copolymerizationmonomers are selected from pyrrole, thiophene, amine functionalthiophene and any mixture thereof.
 7. The electrically conductivepolyaminopyrrole polymer network of claim 2 wherein the conjugatedpolyketone crosslinker is selected from the group consisting ofbenzoquinone, naphthoquinone, anthraquinone, the CN and Cl derivativesthereof, and mixtures of any of them.
 8. The electrically conductivepolyaminopyrrole polymer network of claim 1 comprising electricalconductivity enhancing dopant.